The present invention relates generally to lasers and in particular to controlling fiber coupling between a laser, an on chip modulator and an optical output.
Tremendous amounts of data can be transmitted quickly across a fiber optic or free space link using lasers. This is typically accomplished by modulating the lasers. In one technique, a single laser is turned on continuously and a modulator is used to modulate the light with an input data signal. Using an external modulator rather than changing the intensity of the laser directly leads to reduced parasitic FM modulation or chirp of the signal.
Additionally, coupling the light from the laser, to the modulator, and then to the output fiber, and making sure that this tight coupling is maintained through life of a transmitter is challenging and adds to the cost of such transmitters. In general, any fiber coupling is a costly and time consuming process, on account of the very small optical modes in single mode waveguide devices. Thus, very tight submicron tolerances are often required in the packaging. Typically, when the fiber coupling is maximized, the optical elements are permanently fixed in position. The process is often not very reproducible due to contraction in epoxies or thermal expansion of the components.
Integrated electro-absorption modulators have been very successful recently for a range of medium performance applications. Compared to directly modulated lasers, they have considerably reduced chirp and can be used for longer distance communications. However, the feedback between the integrated modulator and the laser induces, sometimes, unacceptable amounts of chirp for the most demanding applications.
The present invention provides an adjustable optical coupling systems and methods for tunable lasers and on-chip modulators. In one aspect of the invention, one or more lasers are provided on a chip with one or more modulators. One or more optical elements are also provided, such that light from a laser is directed into a modulator by at least one optical element. In another aspect of the invention, a controller is also provided and is coupled to the at least one optical element and configured to adjust the at least one optical element to maximize output power of the light directed into the at least one modulator. In yet another aspect of the invention, another at least one optical element is provided and also an optical output, such that light from a modulator is directed into the optical output by the other at least one optical element.
In a further aspect of the invention, another at least one optical element is provided between the laser or lasers and the modulator or modulators. The optical element is a faraday rotator, in one instance, and an eighth-wave plate, in another. In one aspect of the invention, a polarizer is also provided between the at least one laser and the at least one mirror. In another aspect of the invention, the one or more modulators are fabricated without using selective area growth.
Also, in one aspect of the invention, emitting means for emitting light and modulation means coupled to the emitting means are provided. Furthermore, optical means for directing light having a particular wavelength from the emitting means into the modulation means is also provided. In another aspect of the invention, control means coupled to the optical means and for adjusting the optical means to maximize output power of the light directed into the modulation means is also provided.
Additionally, in another aspect of the invention, a process is provided in which at least one laser on a chip is selected. The at least one laser emits light. Also, an optical path from the selected laser to at least one modulator on the chip is established and the optical path is adjusted to adjust output power to and from the at least one modulator. Also, in one aspect of the invention, the at least one modulator is selected from an array of modulators based on the laser selected and/or on a specific chirp value.
Many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings.